Free air fan



Feb. 10, 1953 G. H. KOCH 2,628,019

FREE AIR FAN Filed Feb. 9, 1951 2 SHEETS-SHEET l WITNESSES:

(ELI-Lia? Patented Feb. 10, 1953 'UNITED STATES PATENT OFFICE.

Gustav H. Koch, Springfield, Mass, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 9, 1951,. Serial No. 210,129

. -1 This invention relates to propeller fans, and relates more particularly topropeller fans of the type known as free air fans which are not connected to ducts or heat exchangers, but which draw air from, and discharge air into, open spaces.

Propeller fans of the free air type are widely used. for ventilating and cooling spaces by the movement of large volumes of air therethrough. However, their adaptation to larger spaces has been limited because of the limitation in the distance from the fan that the air discharged from the fan maintains a given velocity, such as 100 feet per second. Such distance is known as the depth of penetration of the fan.

When a propeller is in operation, each particle. of air, struck by a rotating blade, starts on in a direction which makes a considerable angle with the axial direction. The average angle for all particles leaving the propeller of household fans is about 30. Because of mass inertia, each particle tends to maintain its initial direction in a straight line so that, except for the pressure influences following Bernoullis law, the air delivery would be in the form of a fiat expanding cone having very little penetration. This expansion directly in front of the blade is modified by static pressure diiierences in the planes at right angles to the central propeller axis with the result that the air stream is forced to spiral about this axis. This spiral still retains the expansive forces of inertia and can maintain only limited penetration.

The object of my invention is to provide an improved fan of the free air propeller type.

A more particular object is to provide a fan of this type which effects greater depth of pene' tra-tion; that is, a fan which causes the air discharged therefrom to maintain a given velocity for a greater distance from the fan.

It has been proposed to provide vanes on the discharge side of the propeller blades to change the direction of the air particles so that they all move in paths parallel to the axis. Such vanes remove the disruptive expansion component of the air velocity and convert it into axial velocity so that a substantially increased depth of penetration is effected.

In my application, Serial No, 768,686, filed August 14., 1947, I disclose a fan provided with a group of annular shroud rings surrounding the propeller in concentric relation. These rings are curved in cross section and are shaped. anddisposed so as to direct the side air from directions radially inward to directions forwardly of the blade. This type of fan provides substantially increased volume of air 'flow. It has a lesser depth of penetration than a fan without such shroud rings. Such type of fan has been found well suited. for use adjacent-a window to-sxhaust 3 Claims. (Cl. 230 -7274) air from. a room throu h th wind w, in whic c e e depth f penet ation s. o Of mportance. However, because or it lesser depth of penetration, this fan is not suited for efiecting movement through as large a room. Because of such different characteristics making them suitable for different applications, it would naturally be considered that th spin removing vanes and the annular shroud rings relate to different and inconsistent types of fans.

In accordance with my invention, I provide a fan of the propeller type having both the s in removing vanes and the annular shroud rings. It would be expected that the shroud rings would reduce the depth of penetration of a fan having the spin removing vanes. I have dis? covered, however, that, the depth of penetration is much greater than that of a fan having the spin removing vanes only.

The invention will now be described with reference to the drawings, of which:

Fig. l is a perspective view of a fan embodying this invention;

Fig. 2 is an elevation-a1 side view, mainly in section, of the fan shown in Fig. 1;

Fig. 3 is a perspective view of the spin removing vane assembly of the fan;

Fig. 4 is a cross sectionalview of one of the spin removing vanes, the section being taken along the line 4 4 of Fig. 2;

Fig. 5 is another cross-sectional view of one of the spin removin vanes, the section bein taken along the line 5*5 of Fig. 2'; and

Fig. 6 is a diagrammatic view illustrating the approximate paths of air now developed in the operation of a .fan embodying this invention.

The fan illustrated comprises the similar propeller blades I0 mounted on the shaft of and driven by an electric motor ll supported within the shroud ring assembly l2 by the U-shaped, tubular frame section t3, the latter being carried on the base I4. The blades I 0 may be of any suitable shape.

The shroud ring assembly 12 may be, and in the illustrated embodiment is, the same as that shown and described in my above-mentioned application Serial No. 768,686. .11: comprises a plurality of parallel shroud rings 15,, I6, ll, 18 and. [9 which are axially spaced apart, and are supported on the four straps 20 carried by the. frame section [3. .Thestraps 20 are arranged parallel to. therotary axis of the fanand support the motor I l by means of the brackets 2|, which have radially extending. arm portions secured by bolts to their respective. straps. The brackets 21 may .be riveted or otherwise suitably secured to the housing of the. motor .I .1.

Each of the shroudrings 5, l6, l7, l8 andlii may be rolled or otherwise formed from strip stock. Referring to .Fig. .2 of'the drawin s, .and

to the shroud ring l5 by way of example, the strip forming the ring is rolled to provide a body portion a of arouate cross-section, and terminating in a forward end 12 of minimum diameter and in an opposite end of maximum diameter, the latter being further provided with an inverted annular roll or curl defining a shallow channel. Each of the straps 20 is spot welded to the adjacent portion 1) of the shroud rings.

The shroud rings are disposed concentrically around the fan blades ill with the forward rin 15 located in part forwardly of the blades, and with the rearward rings i8 and I9 located rearwardly of the blades. The rings are preferably mounted in non-overlapping relation, with adjacent edges disposed in the same plane, and with their respective ends is disposed forwardly of the arcuate portions 11 and the outer ends 0. The inner surfaces of the shroud rings are spaced outwardly from the fan blades so that an annular flow passageway 23 around the blades is provided for facilitating unobstructed forward flow of air tending to be drawn radially inwardly of the fan blades, and directed axially by the shroud rings.

For closing the rear end of the shroud ring assembly i2, there is provided a disc-shaped screen 2% which is snapped in the channel 0 of the ring I?) with a rubber strip 25 therebetween.

The spin removing vane assembly 21 comprises a molded plastic member including the outer annular ring 28, the inner annular ring 29 and the spaced spin removing vanes 86 extending therebetween and formed integral therewith. The forward end of the ring 28 is turned backwardly so as to form a channel Si. 32 extends around and in contact with the outer surface of the ring 28. The inner end of the bezel has a diameter slightly less than the diameter of portion 1) of the forward shroud ring l5, and is provided with an annular head 34 which is adapted to be snapped into locking engagement with suitable embossed or raised portions formed on the respective straps to at the points indicated by the reference characters 35.

The vanes 30 are shaped so that, as illustrated by Fig. 6 of the drawings, their leading edges d are substantially parallel to the direction of the rotating air leaving the fan blades and their trailing edges 6 are parallel to the axis of rotation, while the surfaces between the leading and trailing edges are shaped so as to change the direction of air flow to an axial one at the trailing edges. As will be noted particularly from Figs. 4 and 5, each vane 30 comprises in cross section a curved portion extending from the leading edge (1 to an intermediate point ,1 and a flat section extending from the point I to the trailing edge e and tangent to the curved portion. The radius of the curved portion and the width of the curved portion and of the flat portion increase gradually from the inner ring 29 to the outer ring 28.

As illustrated best in Figs. 2, 4, and 6 of the drawings, the chord or width of the vanes, that is, the straight line distance from leading edge to trailing edge, increases from a minimum at the inner annular ring 29 to a maximum at the outer annular ring 28. This increase in chord corresponds roughly to the increase in space between vanes. The vanes 30 have longitudinal axes which intersect substantially at the fan axis and which diverge towards the fan blades, so that their leading edges along their lengths are spaced approximately the same distance from the forward edge of the path swept by the fan blades, thus removing the spin from the air close to the The annular bezel Operation In operation, when the fan blades Ill are rotated by the motor 1 I, a primary volume of air is drawn from the rear of the fan through the screen 24 to the inlet side of the blades. At the same time, as indicated diagrammatically by Fig. 6 of the drawings, a secondary volume of air is drawn radially inwardly from the circumferential region surrounding the fan blades and impinges upon the arouate surfaces a of the respective shroud rings of the assembly 12 and is deflected thereby from radially inward directions to axially forward directions. The secondary air flows through the annular passage 23 and partly through the region inwardly of the blade tips, which is swept by the fan blades. The annulus of secondary air surrounds the primary air. A portion of the how of secondary air, that which strikes the shroud rings 18 and i9, is effected by the negative pressure created by the fan blades, while the flow of the secondary air which strikes the shroud rings 15, iii and i? is induced by the flow of air. discharged by the fan blades.

As air enters the region swept by the blades, it is propelled in a generally axial'direction. However, the. particles of air are not directed in directions exactly parallel to the axis. The various particles are directed in different directions but the average direction of movement of the particles of air struck by the fan blades is at an angle to the axis, in the direction of rotation of the fan blades, as represented by the arrow g in Fig. 6. In the illustrated embodiment, this angle is approximately 30 degrees to a direction parallel to the axis. Thus, the particles are directed in directions diverging from the axis in the form of a cone. In other words, the air leaving the blades has a spinning component of motion. The low pressure produced by the moving air, in accordance with Bernoullis law, reduces the divergence somewhat, but nevertheless, without the vanes 30, the volume of air diverges substantially and rapidly loses velocity.

The spin removing vanes 30, however, deflect the air from the direction in which it is discharged from the fan blade to a direction parallel to the axis. Thus, the air leaving the vanes 33 tends to remain concentrated in a column extending along the axis of rotation of the fan. There is, of course, some divergence of the air as it reaches distances remote from the fan, but the divergence is not nearly as great, thereby maintaining a substantial velocity of air for a much greater distance from the fan.

The following table shows the performance of a 16" fan using the same motor and blades, with and without shroud rings and spin removing vanes:

It will be noted that the addition of the spin removing vanes without the shroud rings results in an increase in penetration of 17.2 feet, and that the addition of the shroud rings without the spin removing vanes results in a reduction in penetration of 7.3 feet. From this it would be expected that the addition of the shroud rings to the fan equipped with spin removing vanes would cause a reduction in penetration. On the contrary, this addition causes an increase in penetration of 14.8 feet. While the reason for this is not clearly understood, the most likely explanation that I have to olfer involves two known effects of the shroud assembly:

1. The shrouds lower the maximum air velocity in the air stream and reduce the concentration of the stream. As a result, the velocities across the larger air stream are more uniform.

2. The shrouds increase the total volume or rate of moving air measurable at a limited distance in front of the blades.

I can only conclude that the air straightening vanes are more effective when they act upon a larger volume of air having a more uniform velocity distribution. The reduction in power input shows less load on the fan motor when the shroud rings are used, and this indicates less turbulence and more efiicient flow.

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications with out departing from the spirit thereof.

What I claim is:

1. A free air fan comprising a rotatable shaft, a plurality of propeller blades mounted thereon, a plurality of annular shroud rings disposed in concentric relation with respect to said blades, said shroud rings having concave outer surfaces which are curved from generally radially inward to substantially axially forward, the forward edge of each shroud ring being disposed adjacent the plane of the rearward edge of the next shroud ring, the discharge edge of one shroud ring being disposed within the axial extent of the fan and as far rearwardly as the tip of the fan, and two others of said shroud rings being disposed rearwardly of said one shroud ring, and a plurality of spin removing vanes disposed adjacent said propeller blades on the front or discharge side thereof, said vanes extending substantially radially in the path of the air discharged from the blades and having a cross section, including a discharge edge disposed substantially parallel to the axis of rotation, for deflecting the air discharged from the blades from a direction having a substantial rotational component to a direction substantailly parallel to the axis of rotation of the blades.

2. A free air fan comprising a rotatable shaft and a plurality of propeller blades mounted thereon, a plurality of annular shroud rings disposed in surrounding concentric relation with respect to said blades, said shroud rings having concave outer surfaces which are curved from generally radially inward to substantially axially forward, the forward edge of one shroud ring being disposed adjacent the plane of the rearward edge of the next shroud ring, and a plurality of spin removing vanes disposed adjacent said propeller blades on the front or discharge side thereof and in the path of the air discharged therefrom, said vanes extending substantially radially and in cross section having inlet edges extending substantially parallel to the direction of flow of air discharged from said propeller blades and outlet edges extending substantially parallel to the axis of rotation of said propeller blades, said vanes being curved between said inlet and outlet edges to change the direction of flow of air to parallel to the axis of rotation.

3. A free air fan as set forth in claim 1 wherein the spin removing vanes have chords which increase as their distance from the axis of rotation increases.

GUSTAV H. KOCH.

- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 697,448 Coleman Apr. 15, 1902 751,325 Morgan Feb. 2, 1904 2,070,875 Weber Feb. 16, 1937 2,231,746 Ballentine Feb. 11, 1941 2,258,731 Blumenthal Oct. 14, 1941 2,441,737 Welch May 18, 1948 2,555,576 Criqui June 5, 1951 

